A STUDY ON THE SUITABILITY OF GLUCOSE UPTAKE
MEASUREMENTS FOR ASSESSING THE CONDITION OF
ACTIVATED SLUDGE AT A WASTEWATER TREATMENT
WORKS
Paul Notcutt
eThekwini Water Services, Laboratory Division, P.O. Box 1038 Durban 4000
Tel: (031) 3024789 Fax: (031) 3034747
E.-mail:[email protected]
INTRODUCTION
The activated sludge of a wastewater works is comprised of various flora and fauna which
alter the nutrients in the raw sewage during the aerobic phase, thereby breaking down
complex organic compounds into carbon dioxide, water and other simple molecules.
Wastewater is biologically treated to produce an effluent that will pass the general or
special permit standards set by the Department of Water Affairs and Forestry (DWAF) and
is suitable for discharge to a receiving water. In order to achieve a good quality effluent,
the activated sludge plant must be working at optimal activity. The activity of the organisms
may be affected by incoming deleterious substances or by inappropriate works operation.
There are a number of chemical and biological methods for measuring the viability of the
activated sludge. The aim of this project was to assess the use of glucose uptake by the
activated sludge to measure the viability or health of activated sludge. The idea for this
test was obtained from a book, Activated Sludge Treatment of Industrial Wastewater,
(1995), page 101.
This investigation was carried out to determine whether the glucose uptake levels of
activated sludge could be related to other analytical results and to observations on the
general condition of the works. As glucose uptake is a basic metabolic function, the
viability of the organisms in the activated sludge could be expected to be reflected by their
uptake performance. In order to establish a baseline of activity, tests were carried out on
the activated sludge from a treatment works which regularly performs well. Tests were
also performed at a works which frequently experienced treatment problems.
METHODOLOGY
Phenol solution (5%m/v).
Glucose working standard solution : 40mg/L.
Sterile Ringers solution : 2 Ringers tablets, were dissolved in 1L of water. The solution
was sterilized at 121°C for 10 minutes
A glucose calibration curve was obtained on the spectrophotometer. Wavelength : 485nm.
Calibration range : 0 to 50 mg/L.
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Glucose uptake
Blank : The activated sludge was filtered and then washed with a sterile buffered solution.
This was to remove any residual sugar initially present in the activated sludge.
Approximately 50ml of activated sludge were filtered and then washed with 30ml of sterile
buffer. .
50ml of Ringers buffer was added into a sterile bottle.
0.1mg of filtered activated sludge was added.
3 drops HCl (conc) was carefully added to the bottle. This prevented the uptake of any
glucose.
5ml of glucose working solution was then added. The bottle was incubated for 1 hour in a
shaking water bath.
Samples : Samples were prepared in the same manner as the blank, except that the conc.
HCl was added after the 1 hour incubation to allow the glucose to be consumed by the
sludge.
2mls of the incubated samples (and blank) were transferred to test tubes.
1ml of the 5% phenol solution was added to each test tube followed by 5ml conc sulphuric
acid.
3ml water was added. The test tubes were allowed to stand and cool for 20mins.
The absorbance of each sample and the blank was read on the spectrophotometer at
485nm.
This method was adapted from Eckenfelder (1995) and combined with method C360 of the
eThekwini Water Services Laboratory.
Total solids
The total solids of each activated sludge sample was analysed as per STANDARD
METHODS (1998). This result is required to calculate the glucose uptake of the samples
per 100g.
RESULTS AND DISCUSSION
The Umbilo Wastewater Treatment Works and Umhlanga Wastewater Treatment Works
were selected as the sample sites. Umbilo WTW receives effluent from domestic and
industrial sources. This works has operational problems due to the inconsistency of the
strength of the raw effluent received. The Umhlanga WTW receives almost exclusively
domestic effluent, the only problems are related to high seasonal peak flows during
holidays.
A comparison was made between glucose uptake data on activated sludge samples and
the results of selected tests performed on the final effluent of each WTW sampled on the
same day. The tests selected were chemical oxygen demand (COD), ammonia (NH4) and
nitrate (NO3). In addition, the glucose uptake data was compared in a qualitative manner
to the findings of the microscopic assessment of the activated sludge sampled.
Microscopic analysis rating
In order to correlate the quality of the activated sludge determined by microscopic analysis
and the glucose uptake, the activated sludge was given a rating. The rating of 1 was given
for poor sludge, 2 was given for an average activated sludge and 3 for a good activated
sludge.
The following would be the general description of the activated sludge with a rating = 1;
(a) there would be little protozoal activity,
(b) the sludge would not have a balance between floc and filament,
(c) one type of filament may have started to dominate,
(d) the floc may have been pinpoint with very few filaments.
The following would be the description of the activated sludge with the rating = 2;
(a) the activated sludge would have a small amount of protozoa activity,
(b) there may have been signs of one type of filament starting to become dominant,
(c) the flock may have been starting to become pinpoint.
The description of the activated sludge given the rating = 3;
(a) there is a balance between floc and filament,
(b) there is more protozoal activity.
The method of rating the sludge was compiled only as a means of comparison with the
glucose uptake data. It was assumed that a correlation might exist between the visual
condition of the sludge and the glucose uptake.
Umhlanga WTW
Nine samples of activated sludge and final works effluent were collected from Umhlanga
WTW. Umhlanga WTW is an extended aeration plant treating ± 8000 kl/day.
Table 1 presents the correlation statistics where nitrate, ammonia and COD results as well
as the microscopic analysis rating were compared to the glucose uptake results.
Table 1 : Correlation co-efficients for Umhlanga WTW data
Sample
Correlation
Glucose uptake & nitrate
0.92
Glucose uptake & microscopic analysis
0.82
Glucose uptake & ammonia
_0.69
Glucose uptake & COD
0.28
Figure 1 displays the results of the ammonia, nitrate and glucose uptake for Umhlanga
WTW.
Figure 1 : Umhlanga W T W .
Glucose uptake vs. Nitrate and Ammonia results
Figure 1: Umhlanga WTW. Glucose uptake vs. Nitate and Ammonia results
NOTE that this graph and others which include glucose uptake results have been ordered
to display the glucose uptake results from lowest to highest. This was done in order to
highlight any trends that may occur in the correlation between glucose uptake and the
other tests.
The correlation between the glucose uptake and the ammonia and nitrate concentrations
was most successful. The graph of ammonia concentration to glucose uptake did follow a
trend. When the activated sludge was under stress the ammonia was not oxidised to
nitrate by Nitrosomas and Nitrobacter. When the activated sludge was viable the
ammonia concentration was lower.
Refer to figure 1. The correlation between the
glucose uptake and nitrates was directly proportional. When the activated sludge was less
viable, the oxidation of the ammonia to nitrates by Nitrosomonas and Nitrobacter was
suppressed and the ammonia concentration was higher.
Figure 2 depicts the correlation between glucose uptake and microscopic analysis for
Umhlanga WWTW
Figure 2 : Umhlanga WTW. Glucose uptake vs. microscopic rating
The correlation between the glucose uptake and microscopic analysis for Umhlanga WTW
was very good. When the activated sludge was less viable, the microscopic analysis
rating was poor and the glucose uptake was suppressed. When the activated sludge was
viable the converse was true. It could be seen from the graph that the microscopic
analysis rating and glucose uptake follow a general trend.
Figure 3 : Umhlanga WTW. Glucose uptake vs. COD
The relationship or correlation between glucose uptake and COD for Umhlanga WTW is
shown in figure 3. The correlation between the glucose uptake and COD would be
expected to be a negative correlation. When the activated sludge was non viable, ie when
there was a low glucose uptake, the COD concentration of the final effluent should be
higher, reflecting treatment problems. No explanation for the correlation and trend
observed can be made at this time.
Umbilo WTW
Umbilo WTW is a conventional waste water treatment works. It receives about 15 mega
litres a day of mixed domestic and industrial effluents of variable strength. Table 2 lists the
calculated correlation co-efficients for the results obtained at Umbilo WTW. A total of 32
data sets were obtained.
Table 2 : Correlation co-efficients for Umbilo WTW data
Sample
Correlation
Glucose uptake & nitrate
0.53
Glucose uptake & microscopic analysis
0.62
Glucose uptake & ammonia
_0.45
Glucose uptake & COD
-0.34
Figure 4 illustrates the correlation between glucose uptake, ammonia and nitrates for the
Umbilo WTW.
.
Figure 4 : Umbilo WTW. Glucose uptake vs. Nitrate and Ammonia results
It can be seen from Table 2 and Figure 4 that the expected inverse correlation between
ammonia and glucose uptake was present. Table 2 indicates fair correlation co-efficients
for ammonia and nitrate. However the graph does illustrate very random data on
occasions. This was probably due to the nature of incoming effluent, namely varying
mixtures of domestic and industrial.
Figure 5 depicts the correlation between glucose uptake and the microscopic analysis for
Umbilo WTW.
Figure 5 : Umbilo WTW. Glucose uptake vs. microscopic rating
The correlation between the microscopic rating and the glucose uptake was 0.62. This
indicated that the microscopic rating followed the glucose uptake trend.
Figure 6 depicts the correlation between the glucose uptake and COD for Umbilo WWTW
Figure 6: Umbilo WTW. Glucose uptake vs. COD
The COD results generally followed the trend of the glucose uptake. The correlation
between the glucose uptake and the COD was -0.34. When the activate sludge was non
viable the COD concentration of the final effluent was unacceptable in terms of the
discharge permit.
As the glucose uptake improved, the COD of the final effluent
improved.
CONCLUSION
In view of the results obtained it is clear that the glucose uptake test could be used
successfully to measure the health and viability of the activated sludge at a wastewater
treatment works. The test is relatively simple and inexpensive to perform and with routine
use will clearly indicate when the activated sludge is under stress.
ACKNOWLEDGEMENTS
The author would like to thank the staff of eThekweni Services Laboratory who contributed
to the work presented in this paper. Frank Stevens (Director), eThekwini Wastewater
Management is thanked for granting permission to present this paper.
REFERENCES
1.
ECKENFELDER W. W. and MUSTERMAN J. L., Activated Sludge Treatment of
Industrial Waste Water, Technomic Publishing Company INC, Pennsylvania, (1995).
2.
Method C360, Sugar in Water, eThekwini Water Services Laboratory,
Manual.
3.
STANDARD METHODS FOR THE EXAMINATION OF WATER AND WASTEWATER,
APHA, AWWA, WEF, 20th Edition (1998).
Methods